There have been a number of projects over the PowerPC OS X years where people have replaced the stock version of Samba with the standard version. It is for Linux and Unix.If all that is needed is SMB3, then we can try building samba4 for PPC.
This was something I was going to try on the work Macs at one point. My problem was that this was a work computer, critical to my job. Screwing up the install or doing something wrong could have meant it not being able to connect to the network at all. And all our files were on the network. At the very least that would have forced a complete reinstall of the OS, apps, settings, etc just to get back to where I was.
A very big undertaking when your deadlines specify delivery of two newspapers and all their content each week.
I found DAVE (Thursby Software) and installed that.
Samba is open source. Go for it if you want.